Torque limiting valve handles are in wide use in petrochemical or other industries wherein hazardous and/or combustible materials are involved. The valve handles are equipped with means for limiting the torque that can be manually applied through the valve stem to prevent damage to the valve and possible accidents involving the hazardous materials.
U.S. Pat. No. 3,441,115, which issued to Gunther, shows such a torque limiting valve handle having a handle housing threadedly engaged with a cap portion. A ball retainer is adapted for mounting on a valve stem and is constrained between the housing and cap portion. A plurality of balls are carried within longitudinal openings in the ball retainer and urged by a stack of Belleville washers into engagement with multiple depressions in an inner surface of the handle housing. The valve handle will rotate as a unit when a torque is applied below a predetermined level. When a torque is applied below a predetermined level, such as when the valve is in a fully open or closed position, the force of the Belleville washers is overcome and the balls are forced out of engagement with the openings. This allows the handle housing and cap portion to rotate independently of the ball retainer and valve stem and prevents excessive torque from being applied to the valve. Adjustment of the force exerted by the Belleville washers is provided by relative rotation of the handle housing with respect to the cap portion and secured by two externally accessible set screws.
However, Gunther and similar conventional designs suffer from several limitations. First, since the adjustment means is externally accessible, unauthorized personnel are able to change the level of force exerted by the Belleville washers to a level which may allow damage to occur to the valve. This may occur intentionally or unintentionally, but in either case, it is undesirable. Secondly, the use of common Belleville washers in contact with all of the ball elements prevents independent adjustment of the force acting on each of the balls.
Therefore, it is a principal feature and advantage of this invention to provide an improved torque limiting valve handle in which adjustment of the torque limit is not possible while the handle is mounted on a valve stem.
It is another feature and advantage of the present invention to provide an improved torque limiting valve handle in which the force exerted on each of the balls is independently adjustable.
It is still another feature and advantage of this invention to provide an improved torque limiting valve handle that permits the operator to temporarily overcome the slippage of handle to valve stem should the slippage not be caused by intentional torque limiting, but by wear or unintended improper adjustment of the torque limit.